1. Field of the invention
The invention concerns an automatically configurable optical system for connecting customer premises networks to a switching center of a telecommunication network. An optical system of this kind comprises an optical distribution network comprising optical fibers coupled to equipments called central office termination equipments in the switching center and coupled to the customer premises networks. The switching center and the telecommunication network are broadband systems. Copper cables are ill suited to transmission of data at high bit rates which is why optical fibers are used to connect the customer premises networks to the switching center. To facilitate the adoption of a connection system of this kind it is necessary to minimize the cost of implementing each customer premises network and to ensure that services are extremely reliable.
2. Description of the prior art
French patent application n.degree. 91 12 264 describes an optical connection system in which each central office termination equipment comprises an optical sender and an optical receiver operating at the same fixed wavelength. Each central office termination equipment uses a different wavelength. Each customer premises network comprises an optical sender and an optical receiver which can be tuned to different wavelengths. A wavelength is assigned to a customer premises network by a control unit in the switching center at the time each call is set up between the customer premises network and a central office termination equipment. The number of customer premises networks is very much larger than the number of central office termination equipments to which they are connected because not all customer premises networks make or receive calls simultaneously. Dynamic assignment of wavelengths to customer premises networks means that the same wavelength can be used again for different customer premises networks setting up non-simultaneous calls.
A group of customer premises networks is connected to a group of central office termination equipments by a distribution network which broadcasts an optical signal sent by any sender of the connection system to each optical receiver of the connection system. A switching center may comprise a plurality of identical connection systems each comprising a group of central office termination equipments connected to a group of customer premises networks by independent broadcast networks so that a common set of wavelengths can be re-used several times.
A control central office termination equipment in each group of central office termination equipments sets up calls. When a customer premises network goes active, it sends a message using the control central office termination equipment wavelength. The control central office termination equipment sends the message to the control means of the switching center. The control means tell the control central office termination equipment the identity of a central office termination equipment available to set up a call. The control central office termination equipment sends a message to the customer premises network using the control central office termination equipment wavelength. This message tells the customer premises network the identity of the available central office termination equipment. The customer premises network deduces from this the wavelength at which it must send and receive to use the central office termination equipment assigned to the call. This wavelength is assigned to this customer premises network for the entire duration of this call, and for this duration only.
In order to function a customer premises network needs to know the control central office termination equipment wavelength and the relationship between the identities indicated in the messages sent by the control central office termination equipment and the wavelengths. In this prior art system a customer premises network can know this information only if it is provided when it is installed. For example, it is feasible to program this information manually into the customer premises network by means of small switches or by plugging in a read-only memory module. This type of method has the drawback of requiring a certain amount of work each time that a customer premises network is installed and lacks flexibility because it is not possible to replace a faulty central office termination equipment with another central office termination equipment having another wavelength without doing the same work over at all customer premises networks. In particular, it is not possible to assign the control central office termination equipment function to any of the central office termination equipments installed in the switching center. If a central office termination equipment fails it must be replaced with another central office termination equipment having the same wavelength. Consequently, either a large number of central office termination equipments having predetermined wavelengths must be kept in reserve or a single central office termination equipment must be kept in reserve having a wavelength which is set when it is put into service.
An object of the invention is to propose a connection system that is configurable and reconfigurable automatically to avoid the need for work on each customer premises network when the latter is installed and to minimize the disturbance to services in the case of a fault in a central office termination equipment or in the distribution network.